The increased interest in use of trailers as a part of a recreational vehicle combination has introduced to the owners of such trailers the problem of maintaining stability of the towing vehicle as well as the towed vehicle while in transit. The problem is two-fold in that not only is the trailing vehicle occasionally found to be swaying back and forth behind the towing vehicle, "fish-tailing" as it is called, but the driver of the towing vehicle may suddenly realize that his own vehicle is being caused to sway back and forth by the action of the trailing vehicle behind it.
Generally speaking, the forces which initiate this swaying of either the trailing vehicle or the towing vehicle are external and can be encountered either from the rear or from the front. For example, when an approaching large truck or bus comes upon the towing vehicle, there is a force from the air created by the passage of the oncoming vehicle which first strikes the towing vehicle. This causes the towing vehicle to suddenly tend to sway away from the oncoming vehicle and the driver must apply proper recovery effort. Then as the oncoming vehicle passes the trailing vehicle, the driver of the towing vehicle then experiences a whipping action as a result of the trailing vehicle being pushed sideways by the force of the air due to the passage of the oncoming vehicle. In the first instance, as the driver attempts to keep the towing vehicle in a straight path, this motion back toward the center line of the side of the highway upon which the vehicle is being driven imparts a reverse directional movement to the trailing vehicle. That is, as the car is pushed to the right by the oncoming vehicle, the trailing vehicle is directed toward the left as a result of the movement of the car's rear end toward the path of the oncoming vehicle. As the driver of the towing vehicle then directs his vehicle back to the left, this imparts a motion to the trailing vehicle to go to the right. As a result of this right and then left movement of the towing vehicle and the ensuing left and then right movement of the trailing vehicle, there is imparted to the combination a sinuous or "fish-tail"-like movement between the two vehicles which, if not dampened properly, can result in a development of a increasing moment of fish-tailing or deviation which can result in a serious accident.
In the second part of the application of force by the oncoming vehicle as the air pressure is directed against the trailing vehicle, this in turn causes the trailing vehicle to be directed to the right which imparts a tendency to force the towing vehicle to the left. In some instances, if the change of direction of the trailing vehicle by the action of the towing vehicle is sufficient, it is possible that the air pressure from the oncoming vehicle will cause the trailing vehicle to attempt to move more directly toward the oncoming vehicle because of the air pressure acting upon the rear part of the trailing vehicle and giving that part of the trailing vehicle a vector to the outside as well as a vector forward. In this latter instance, the moment of deviation created by this tendency of the trailing vehicle to move opposite to the direction of the towing vehicle can produce a more serious situation than occurs in the instance when the towing vehicle itself is the first one to cause the deviation.
In the situation where the towing vehicle and its trailer are being overtaken by a large, fast moving vehicle, the reverse situation occurs. The trailing vehicle is the first to feel the force of the air created by the passage of the passing overtaking vehicle and this initially can cause the rear portion of the trailing vehicle to tend to drift to the right, thus presenting a condition for the driver when he feels that his car is being pulled to the right. As the force of air then approaches the front end of the trailer, the pressure of the air from the overtaking vehicle has a tendency then to cause the rear end of the towing vehicle to also want to slide to the right, thus placing the towing vehicle in an alignment which would tend to interfere with the path of the overtaking vehicle if corrective measures were not taken such as steering the towing vehicle to the right. Then as the overtaking vehicle approaches and passes the towing vehicle, the air pressure again is directed to the towing vehicle in such a manner as to tend to cause it to drift to the right further. Attempts to correct this indicated line of direction of movement again results in the fish-tailing not only of the trailing vehicle but of the combination of the towing vehicle and the trailing vehicle.
High winds from one side of the other can also present the same type of problem to a driver of the towing vehicle because of the fact that the trailing vehicle is more or less a free object being drawn along a highway and is more subject to the lateral wind forces than is the towing vehicle. This can cause the trailing vehicle to begin to sway which sway is then imparted to the towing vehicle and the resulting fish-tailing continues.
Yet another action which can cause the fish-tailing situation to arise is when the driver of the towing vehicle is forced to make sharp turn and counter-turn to avoid an object which suddenly appears in the highway before him.
The conditions which cause the problems set forth before produce even more dangerous problems in those instances in which the trailing vehicle comprises a trailer carrying a boat or a trailer carrying an airplane, particularly sailplane. In these instances the vehicle being carried, be it boat or sailplane is merely resting so to speak in the towing trailer. The trailer itself is of a less sturdy construction than employed with the types of trailers which form living quarters, having smaller wheels and less weight.
Various devices have been developed to attempt to prevent this fish-tailing between the trailing vehicle and the towing vehicle to keep them stabilized in a more or less straight line relationship. Some devices included sets of parallel bars interconnecting the vehicles with springs attached to the bars to provide some measure of taking up the lateral movement moment of either the towing vehicle or the trailing vehicle. However, these were cumbersome and were not entirely satisfactory.
One sway control device which is commercially available utilizes a bar which interconnects the trailing vehicle with the towing vehicle. This device is commercially available by the EAZ-LIFT Spring Corporation. It consists of a first bar which is pivotally mounted adjacent the ball hitch on a towing vehicle. There is a second bar which slides over the first bar. The second bar is pivotally attached to one arm of the normal A-frame trailer hitch. By means of an adjustable braking shoe on the second bar pressure can be put on the first bar to prevent the free movement of the trailing vehicle with respect to the ball hitch of the towing vehicle. Another device to attempt to control sway between the towing vehicle and the trailing vehicle is disclosed in U.S. Pat. No. 2,940,776. This device includes a horizontal plate having an arcuate recess on the underside thereof, the plate being mounted on the A-frame trailer hitch. The underside of the plate which is in contact with the coupling device on the towing vehicle has two flat camming surfaces, one on each side of the recess which extend laterally therefrom. These camming surfaces are flat and are inclined slightly downwardly when the device is in use. The coupling device is placed in the recess and then is retained therein by a spring biased nut and bolt assembly which exerts pressure on the coupling device to force it into contact with the recess. While the coupling device will move out of the recess upon the turning of an angle between the towing vehicle and the trailing vehicle, such movement is resisted by the spring biased element.
Other devices which disclose means for centering a trailing vehicle behind a towing vehicle are found in U.S. Pat. Nos. 2,110,114 and 2,124,043. While these devices were initially developed in connection with tractors drawing field equipment such as gang plows, disk harrows and the like, the problem was again that of maintaining a straight line between the tractor and the towed equipment. The devices generally comprised a flat tongue member having a slot to provide a lost motion means and a flat cross-bar which is in the form of a U so to speak, which is attached to the towed piece of equipment. The inner surface of the flat bar of the U-shape has a recess of an arcuate form into which is fitted a rotatable disk mounted thereon on the draw bar. As the vehicle is turned the flat disk rotates thus permitting the U-shape member to move left or right with the disk coming out of the recess. If the turn is not sufficient to cause the disk to be completely removed from the recess, then the motion of the towing vehicle returning to a straight alignment with the trailing equipment causes the equipment to come into line more quickly by the pressure of the tendency of the flat disk to return to its centered position in the recess. A modification of this was to provide a spring biasing means for the flat disk and to provide a flat camming surface on each side of the central recess to further permit wider, sharper turns and at the same time assist in returning the towed equipment into straight alignment with the tractor.
In addition to stabilizing the towing vehicle and trailing vehicle to eliminate the tendency for fish-tailing, there is also a problem of jack-knifing of the trailing vehicle about the towing vehicle. This probably more often occurs when backing the trailing vehicle into a certain position, and the towing vehicle forms an angle with the trailing vehicle such that the trailing vehicle no longer moves horizontally but tends to remain fixed and pivot about one of its wheels. Jack-knifing also can occur when travelling at high speed along the highway and making a sharp turn, or when the tendency to fish-tail develops such momentum that the trailing vehicle suddenly appears to be coming up along side of the towing vehicle. Again various devices have been developed for this purpose to prevent this from happening in the use of trailers such as carrying boats or small house trailers. These frequently consisted of a series of interconnecting members such as chains or cables so that the trailer could not get too far out of alignment with the towing vehicle. These of course were cumbersome and a more simplified form may be seen in U.S. Pat. No. 3,580,612. This device comprises basically two flat plates which are pivotal in their relationship to each other. One plate contains a pair of arcuate slots on each side of the pivotal axis. The other plate contains a bolt and nut arrangement which is inserted into the slots. The slots of course limit the amount of relative pivotal movement between the two plates.
The present invention differs from the known prior art in that it utilizes the moment created by the trailing vehicle itself as it begins to deviate from its alignment with the towing vehicle. To accomplish this use is made of a cam and lever arrangement. The cam assembly is attached to the towing vehicle and the lever arrangement is attached to the A-frame of the hitch on the trailing vehicle. The present invention provides that when the trailing vehicle is connected to the towing vehicle and the lever assembly is brought into contact with the cam assembly on the towing vehicle, the lever assembly can be placed under predetermined tension so that the moment created by the trailer's tendency to deviate from the straight line is resisted by the trailer itself and thus the tendency to fish-tail is substantially reduced if not eliminated. The present invention also provides for an adaption to this cam and lever assembly which prevents fish-tailing. This is accomplished by means of a solenoid which activates a pin which enters a slot on the camming place, the solenoid being in turn actuated by the application of a braking pressure from the towing vehicle.